diff --git a/js/WikiTextRules.js b/js/WikiTextRules.js
index 4fe54ee19..c59a893e8 100755
--- a/js/WikiTextRules.js
+++ b/js/WikiTextRules.js
@@ -414,7 +414,7 @@ var rules = [
 				oldNextMatch = w.nextMatch,
 				oldChildren = w.children,
 				oldDependencies = w.dependencies,
-				parseTree = w.store.parseText(mimeType,content);
+				parseTree = w.store.parseText(mimeType,content,{defaultType: "text/plain"});
 			w.output = oldOutput;
 			w.source = oldSource;
 			w.nextMatch = oldNextMatch;
diff --git a/tiddlywiki5/tiddlers/TypedBlockTests.tid b/tiddlywiki5/tiddlers/TypedBlockTests.tid
index f49cfe652..69e55be79 100644
--- a/tiddlywiki5/tiddlers/TypedBlockTests.tid
+++ b/tiddlywiki5/tiddlers/TypedBlockTests.tid
@@ -42,3 +42,14 @@ Which renders as:
 $$$.json
 {"teapot": "brown","inside":["milk","sugar",23]}
 $$$
+
+Unknown types render as plain text:
+{{{
+$$$text/unknown
+Some plain text, which will not be //formatted//.
+$$$
+}}}
+Which renders as:
+$$$text/unknown
+Some plain text, which will not be //formatted//.
+$$$